1. Field of the Invention
The present invention relates to a picking device for sequentially picking a plurality of objects which are randomly piled.
2. Description of the Related Art
For example, in a manufacturing process for an automobile component, the processes of die-casting, machining and assembling of component materials are individually carried out, and each process is carried out in different cycle time. Since each process is carried out at a different area of a product line, the components are often required to be transferred between each process. Therefore, after one process is finished, the processed components are collectively stored in a container or a basket, until the components are supplied to the next process. In particular, since it is usually not a problem for the component materials to have to have a few scratches prior to the machining process, the components are often stored in a “random pile” state.
There are mainly three methods for picking objects such as the above mentioned component materials contained in a “random pile” state in a basket or the like. The first method is to pick and align each object by hand before supplying the object to the next process, or to pick each object and set on a machine tool or the like by hand. However, since this method tends to increase the workload of an operator, the following methods have been used in recent years.
The second method is to attach a magnet to a picking hand such as a robot hand, and to pick each object by putting the hand into a basket containing the object. In this method, a robot is moved randomly or with a certain level of regularity within the basket so as to pick each object. Therefore, the robot hand may be positioned at a region in the basket where the objects do not exist, may unstably grip the object and then drop it or may pick two or more objects at the same time, whereby the reliability and efficiency of the operation is deteriorated.
The third method is to use a vision sensor to assist the picking operation by a robot. Since this method improves reliability of the operation for sequentially picking each object, it has been employed in many cases. For example, Japanese Patent Publication (Kokai) No. 2004-188562 discloses a workpiece picking device having a three-dimensional vision sensor mounted to a robot, in which the vision sensor measures the position and orientation of a specified object among a plurality kinds of object and the robot picks the specified object.
Japanese Patent Publication (Kokai) No. 2-256485 discloses a robot having a vision unit, in which a robot hand picks an object contained in a box.
The device of Japanese Patent Publication (Kokai) No. 2004-188562 is suitable for sequentially picking a plurality of objects which are stacked in a “random pile” state. However, the method disclosed takes a time to pick each object, because first the device requires the height distribution data of the region of interest, then the target objects need to be detected from the captured two-dimensional image, and finally the robot must be moved to align the three-dimensional vision sensor with the target object for obtaining the position and the orientation of the object where yet another detection is made, all before the robot can position itself for gripping one object.
On the other hand, in the device of Japanese Patent Publication (Kokai) No. 2-256485, objects can be picked if a plurality of objects are stacked in a laminar manner and the existing heights of the stacked objects are known. However, when the position and the orientation of the objects are not in order such as in the case of a “random pile” state, the failure of picking may occur, e.g., the gripping position of a robot may be offset and/or a hand of the robot may interfere with another object. For example, as shown in FIG. 8, a robot hand 104 is intended to pick an object 102 from directly above the object, while object 102 is positioned on a view line of a camera 100. At this point, in the case where object 102 is located at position Z2 even though the object is expected to be located at a predetermined position Z1 in relation to the Z-direction, at least one of the X- and Y-coordinates of the gripping position for object 102 is different from the actual coordinates. As such, when an object is to be picked from a “random pile” state in which the existing height of each object is unknown, the picking operation cannot be properly carried out without accurately obtaining the X-, Y- and Z-coordinates of the object to be picked.